Total Synthesis of 6-Deoxy-l-talose Containing a Pentasaccharide Repeating Unit of Acinetobacter baumannii K11 Capsular Polysaccharides

Herein, we report a concise synthetic approach for the first total synthesis of a pentasaccharide repeating unit of Acinetobacter baumannii K11 capsular polysaccharides containing a rare sugar 6-deoxy-l-talose. The pentasaccharide was synthesized in a convergent manner using a [3 + 2] block glycosylation strategy. During this synthetic strive, we used a 2,2,2-trichloroethoxycarbonyl (Troc)-protected monosaccharide unit to achieve a high yield during the glycosylation to synthesize a trisaccharide, and chemoselective deprotection of the Troc group from the trisaccharide was carried out under a mild, pH-neutral condition, keeping the O-glycosidic bond, azido, and acid/base sensitive group intact. A thiotolylglycoside disaccharide donor containing 6-deoxy-l-talose was synthesized for the first time by the armed-disarmed glycosylation method between two thiotolylglycosides.

Synthesis of 2-azido-2-deoxy- and 2-acetamido-2-deoxy-D-manno derivatives as versatile building blocks

Reported herein is the synthesis of a number of building blocks of 2-amino-2-deoxy-d-mannose from common d-glucose precursors.

Total synthesis of sinenside A

The first total synthesis of norlignan glucoside sinenside A has been accomplished. An intramolecular acetalization reaction has been employed as the key skeletal construct to forge the central cyclic disaccharide core. The trans-1,2-diol configuration present in the cyclic disaccharide of this natural product is unique and has been addressed by setting this configuration at the beginning. A 1,2-orthoester group has been selected as a handle for both sp glycosidation and for differentiation of the C2'-OH (that participates in the key acetalization reaction) of the sugar unit.

Synthesis and biological evaluation of phosphono analogues of capsular polysaccharide fragments from Neisseria meningitidis A

Neisseria meningitidis type A (MenA) is a Gram-negative encapsulated bacterium that may cause explosive epidemics of meningitis, especially in the sub-Saharan region of Africa. The development and manufacture of an efficient glycoconjugate vaccine against Neisseria meningitidis A is greatly hampered by the poor hydrolytic stability of its capsular polysaccharide, which is made up of (1-->6)-linked 2-acetamido-2-deoxy-alpha-D-mannopyranosyl phosphate repeating units. Since this chemical lability is a product of the inherent instability of the phosphodiester bridges, here we report the synthesis of phosphonoester-linked oligomers of N-acetyl mannosamine as candidates for stabilised analogues of the corresponding phosphate-bridged saccharides. The installation of each interglycosidic phosphonoester linkage was achieved by Mitsunobu coupling of a glycosyl C-phosphonate building block with the 6-OH moiety of a mannosaminyl residue. Each of the synthesised compounds contains an O-linked aminopropyl spacer at its reducing end (alpha- or beta-oriented) to allow for protein conjugation. The relative affinities of the synthetic molecules were investigated by a competitive ELISA assay and showed that a human polyclonal anti-MenA serum can recognise both the phosphonoester-bridged fragments 1-3 and their monomeric subunits, glycosides 20 and 21. Moreover, the biological results suggest that the abilities of these compounds to inhibit the binding of a specific antibody to MenA polysaccharide are dependent on the chain lengths of the molecules, but independent on the orientations of the anomeric linkers.

1,2-Anhydrosaccharides and 1,2-Cyclic Sulfites as Saccharide Donors in Convergent Synthesis of Glucopyranosyl-, Mannopyranosyl- and Ribofuranosylbenzocamalexin

A convergent synthesis of 1-(β-D-glucopyranosyl)-, 1-(α-D-mannopyranosyl)- and 1-(β-D-ribofuranosyl)benzocamalexin was elaborated as an alternative route to the linear approach based on the indoline-indole method. 1,2-Anhydrosaccharides and 1,2-cyclic sulfites as saccharide donors were used in the key glycosylation step. Coupling with benzocamalexin resulted in moderate to excellent yields of nucleoside analogs, depending on the saccharide donor, catalyst and solvent used.